
		\centering
		\begin{center}
			\begin{tikzpicture}[-stealth,scale=2,transform shape,node distance = 1em]
				\tikzstyle{every node}=[font=\small,scale=0.8]
				\begin{scope}[minimum height = 1pt]
					\tikzstyle{inout}=[trapezium, trapezium left angle=60, trapezium right angle=120, draw] %%输入输出框
					\tikzstyle{point}=[coordinate,on grid,] % 像素点,用于连接转移线
					\tikzstyle{mid}=[rectangle,  opacity=0,draw] 
					\tikzstyle{end}=[rectangle, rounded corners, draw]   %%教材上的起止框
					\tikzstyle{endn}=[rounded rectangle, draw]   %%新版的起止框
					\tikzstyle{exec}=[rectangle, draw]    %%执行框 execute
					\tikzstyle{io} = [trapezium, trapezium left angle=70, trapezium right angle=110, minimum width=3cm, minimum height=1cm, text centered, draw=black]  % 平行四边形
					\tikzstyle{decide}=[diamond,aspect=2,draw,thin]   %%判断框 opacity=0.3
					
					% 节点 直线
					\node[end] (s) at (0,0) {入口};
					\node[decide] (d1) at ([yshift=-2em]s.south) {E};
					\node[exec] (e1) at ([yshift=-2em]d1.south) {执行S1};
					\node[end] (end) at  ([yshift=-2em]e1.south) {出口};
					
					% 右边
					\node[exec] (e2) at ([xshift=3em]e1.east) {执行S2};
					
					
					% 连线 
					\draw (s) -- (d1.north);
					\draw (d1.south) -- node[right]{true}(e1.north);
					\draw (e1.south) -- (end.north);
					
					% % 右边斜线
					\draw (d1.east) -| node[above]{false}(e2.north);
					\draw (e2.south) |- ([yshift=0.6em]end.north);
					
					\begin{pgfonlayer}{background}
						\node [draw=black,fill=white ,dashed,rectangle, inner sep=1.3em,line width=0.0025em][fit=(e2)](box1){};
					\end{pgfonlayer}
					
					%  外部指向框
					\node(a2)[draw, draw=black, fill=white,line width=0.05em, rectangle callout, callout relative pointer={(-0.4,-0.3)}, rounded corners, align=center ,inner sep=0.3em] at ([xshift=1.5em, yshift=1.5em]e2.north) {可选};
					
					
				\end{scope}
			\end{tikzpicture}
		\end{center}
